Pit cofferdam cofferdam is usually divided into soil, soil and steel sheet pile cofferdam. 1. General requirements of pit cofferdam: the top cofferdam should be higher than the maximum water level 0.5m that may occur during construction; compression cofferdam should be adopted for river section anticorrosion measures; cofferdam should be waterproof and sealed to reduce leakage; cofferdam should meet the needs of infrastructure construction sheet pile manufacturers ; cofferdam should meet the requirements of strength and stability. 2. Soil depth is less than 2 m, and flow velocity is less than 0.3 m/s. Small and riverbed scouring are less permeable soils. During construction, according to the actual situation of the first excavation canal of the wharf, station location or temporary cofferdam, the bridge located in the cofferdam should be generated. During construction, debris from upstream to downstream embankments should be cleared first. 3. The suitable depth of soil cofferdam is not more than 3m, and the velocity of flow is less than 1.5m/s. The soil permeability of soil cofferdam to river water is good. Soil bags are usually straw bags, hemp bags or bags. The amount of soil is usually 1/2 to 1/3. Stacking requires jointing each other and stacking as neatly as possible. 4. Steel sheet pile cofferdam uses deep water riverbed as sandy soil, clay, gravel and other soil and weathered rock. Sheet piles are used for circular, rectangular and circular end shapes. Construction scheme of steel sheet pile cofferdam: steel sheet piles are arranged to the prison, and plugs and dragons are installed around the steel sheet piles around the prison. Stamping steel sheet pile method can be divided into blocks (groups) to punch. After the first matching part of dragon is hit, the first matching dragon and part of the first matching dragon are inserted block by block and then hit. 5. Excavation and bottom sealing: The success of cofferdam can be achieved by excavating soil, water point and dry excavation of foundation pit, excavation and excavation methods converge to excavation or not, open excavation, excavation, scouring and suction method.